1. Field of the Invention
The present invention relates to an Organic Light Emitting Display (OLED) and method of fabrication and, more particularly, to an Active Matrix OLED (AMOLED) and method of fabrication.
2. Description of the Related Art
In general, an OLED is an emissive display in which a fluorescent organic compound is electrically excited to emit light therefrom. OLEDs can be classified into passive OLEDs and active OLEDs based on a driving scheme for driving N×M pixels arranged in a matrix form. The AMOLED has a lower power consumption than the passive matrix OLED so that it is advantageously suitable for implementing a large display area thereof and has high resolution.
An AMOLED includes a buffer layer formed on an insulating substrate. An active layer, a gate insulating layer, a gate electrode, an interlayer, and source/drain electrodes are formed on the buffer layer of the insulating layer using typical methods. The source/drain electrodes are in contact with the active layer through a contact hole formed within the interlayer. The active layer, the gate insulating layer, the gate electrode, and the source/drain electrode form a thin film transistor. A passivation layer is formed over the entire surface of the substrate including the thin film transistor, and a via hole for exposing one of the source/drain electrodes is formed within the passivation layer. The passivation layer is an inorganic layer and has bad planarization properties so that it has a groove resulted from patterns below the passivation layer, especially due to topology of the contact hole.
A pixel electrode is then formed to be in contact with the source/drain electrode exposed within the via hole. Since the pixel electrode is formed along the bottom and side walls of the via hole, it is bent within the via hole. A pixel defining layer is then formed to cover the bent pixel electrode within the via hole such that the pixel defining layer has an opening for exposing the pixel electrode at a position spaced apart from the via hole. Then, an organic emission layer is formed on the pixel electrode exposed within the opening, and an opposite electrode is formed on the organic emission layer. The pixel electrode, the organic emission layer, and the opposite electrode form an organic light emitting diode, which is connected to the thin film transistor through the via hole so that it is driven by the thin film transistor.
In the method of fabricating the OLED, the pixel defining layer acts to protect the organic emission layer from being positioned on the bent pixel electrode within the via hole, so that deterioration due to the bent organic emission layer can be prevented. In addition, the topology due to patterns below the passivation layer, especially the topology due to the contact hole can be relaxed to prevent the organic emission layer from being bent or broken above the contact hole.
The pixel defining layer is generally formed of a photosensitive organic insulating layer having good planarization properties, and the photosensitive organic insulating layer contains a sensitizer. When the organic light emitting display is driven, the sensitizer can take a form of outgas to cause the deterioration of the organic emission layer in contact with the pixel defining layer.